The invention relates to an intramedullary nail osteosynthesis system for the multidirectional, angular-stable treatment of fractures of tubular bones.
Intramedullary nailing is a surgical method for treating fractures of tubular bones, in particular the large tubular bones of the upper leg (femur), shin bone (tibia) and upper arm bone (humerus). The intramedullary nail has an elongated nail body consisting of metal that is inserted into the intramedullary space of the tubular bone to bridge the fracture in order to fix the bone fragments during the healing process. After the bone heals, the intramedullary nail can be removed. The rapid mobilization and load-bearing capacity of the patient after the treatment are advantageous.
The method was developed and promoted by G. Küntschner. The method was clinically tested by him during the period of the Second World War and was then accepted worldwide. There have been numerous publications about this method and its improvements. Furthermore, it is the subject of numerous patent applications.
Intramedullary nailing is not considered positively by everyone. Primary criticisms are impairment to intramedullary space circulation, resulting malpositioning and serious infections.
Küntschner first developed an intramedullary nail with a V-shaped cross-section, and he also used an intramedullary nail in the form of a slotted metal tube in order to improve the retention of the intramedullary nail in the tubular bone. The enlarged contact surface between this nail and the tubular bone lead to a transfer of load and force over a greater surface. In order to enhance this effect, the intramedullary space was drilled out. This resulted in additional damage to the bone circulation. In order to enlarge the surface contact between the metal tube and bone, transverse screws at the nail ends can be introduced through the bone. To this end, the intramedullary nails have circular or slotted holes in the ends through which the locking screws can be guided.
Intramedullary nails that have a central through-channel are widespread. A guide wire or guide pin is introduced into the intramedullary space to set the intramedullary nail. The intramedullary nail is hammered into the intramedullary space over the guide element. To do this, a hammering element with a wide head is screwed onto the top end of the intramedullary nail. The intramedullary nail is driven in with a hammer. The guide element ensures that the intramedullary nail enters the other part of the fracture after leaving one part of the fracture.
In order to reduce vascular damage from drilling, so-called unreamed intramedullary nails were used in previous decades. These are solid intramedullary nails that generally do not have any cavity. They consist of solid material and therefore also offer the option of locking.
Intramedullary nails are shaped anatomically. Furthermore, they are available in different thicknesses and lengths. They are preferably manufactured from stainless steel or titanium alloy.
The generic DE 43 41 677 C1, the entire contents of which is incorporated herein by reference, describes a locking nail for treating bone fractures with an elongated body consisting of solid material that is rounded on the front distal end and has a proximal hammering end. Transverse bores are arranged along the elongated body to each accommodate a bone screw. Each transverse bore has a least one funnel-shaped opening that expands outward on one side of each transverse bore. The funnel-shaped openings are for easily guiding a drill bit that is imprecisely placed on the bone and does not precisely mate with the transverse bores through the respective transverse bore. Greater flexibility in the fixation of a locking nail is ensured by a plurality of transverse bores at a distance from each other, for example in the treatment of a comminuted fracture. Due to its small cross-section, the locking nail reduces the hazard of impaired circulation. The known locking nail is weakened by the many transverse bores with the funnel-shaped openings. The weakening exists in particular in the middle of the intramedullary nail which is subjected to the greatest stress. The danger therefore exists of the intramedullary nail breaking under stress.
DE 196 29 011 A1, the entire contents of which is incorporated herein by reference, describes an intramedullary nail that has a through-hole for each locking screw with funnel-shaped expansions on either side and a threaded area in the middle. The transitions between the expansions and threaded area are rounded. The through-holes are formed in inlays which are welded at their cylindrical outer perimeter to the basic material of the intramedullary nail. The basic material and locking screws consist of a titanium with a greater hardness, and the inlay consists of a titanium with a lesser hardness. Consequently, the locking screws can be screwed in at different angles (multidirectionally) while forming a thread into a bore of the bone on both sides of the intramedullary nail as well as into the through holes. This enables multidirectional, angular-stable locking. The reduced intramedullary nail cross-section at the through holes expanded in the form of a funnel weakens the intramedullary nail. Based on this principle, intramedullary nails were produced that have such multidirectionally interlockable screws at the ends of the intramedullary nails. The reduced cross-sections are uncritical at the ends of the intramedullary nails because the intramedullary nail is only subject to comparatively low stress at that location.
EP 1 143 867 B1, the entire contents of which is incorporated herein by reference, describes an intramedullary nail that has at least one through-hole on both sides of the fracture. On both sides, the through hole has areas that expand spherically outward and has a thread-bearing area in the middle. The entire intramedullary nail can consist of a comparatively hard titanium. Locking pins are inserted in the through holes on both sides of the fracture. A locking pin is conical and has threads on both ends for screwing into the bone that consist of a harder titanium material. In between, it has a conical jacket region that consists of a softer titanium material. When screwing in the locking pin through a bore in the bone into a through-hole, the locking pin forms a thread in the bone on both sides of the intramedullary nail, and the thread of the through-hole forms a thread in the jacket region of the locking pin. The locking pin can be screwed with the intramedullary nail with angular stability in different angular alignments. A disadvantage of this intramedullary nail is the weakening of the cross-section in the area of the through-holes that can cause failure under stress. In addition, it was revealed that forming a thread by screwing a soft pin part into a hard female thread is problematic.
Despite the described advantages, the healing process is lengthy, even with intramedullary nailing. During the healing process, the bone can only be subject to limited stress.
Against this background, an object of the invention is to provide an osteosynthesis system with an intramedullary nail and bone screws that more effectively supports the healing process and increases the load-bearing capacity of the tubular bone during the healing process.